David n



(No Model.)

D. N. MELVIN.

COMPOUND STEAM ENGINE.

No. 270,552. Patented Jan.9, 1883.

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' than the packing of the main piston.

UNtrn STATES PATENT rrren.

DAVID N. MELVIN, OF LINOLEUMVILLE, NEW YORK.

COMPOUND STEAM-ENGENE.

SFECIFICATION forming part of Letters Patent No. 270,552, dated January 9, 1883.

Application filed June 24,1882.

pressure, to be explained hereinafter, acts only on an annular surface of the main piston to induce the inward stroke. The same steam is then allowed to flow freely over and act on the whole of the opposite face of the main piston to induce the outward stroke. A single slidevalve proportioned to cut off the steam from the high-pressure side at about two-thirds of the stroke, and carefully proportioned on other points, serves as the only valve required. The extension from the piston of a hollow part of snfficiently-smaller diameter, known as a trunk, carries packing, which maintains a tight joint with theinterior of acarefully-bored cylinder of a sufficient diameter. The packing of the trunk may be identical with but smaller Outside of or nearer to the shaft than the packing proper of the trunk I employ a second packing, which may be lightly-compressed cotton, serving as a lubricatorto hold and spread oil upon the inner surface of the small cylinder. The live steam from the boiler flows into and through a jacket inclosing one or both the cylinders on its way to the steam-chest. I so arrange the passages that the steam circulates over the whole cylindrical area. The transverse pin or bearing in the piston is fixed rigidly to the connecting-rod. Brasses embracing it are set up, as required, by connections from the exterior.

The following is adescription of whatloonsider the best means of carrying out the invention.

The accompanying drawings form a part of this specification.

Figure l is a horizontal longitudinal section. Fig. 2 is a cross-section on the line 8 s in Fig. 1.

(No model.)

Fig. 3 is an end elevation of the peeuliartrunkpiston. Fig. 4 is a side elevation of a modification. It is a double engine.

Similar letters of reference indicate correspondingparts in all the figures.

A is the fixed portion of the engine, certain parts being distinguished, when necessary, by additional marks, as A A B is the main piston or piston proper. B is a hollow cylindrical extension from one face thereof. The main piston B reciprocates in the main cylinderA. Thelatter is surrounded with a casing, A*, at a little distance therefrom, the space between A and (marked a serving as a steam-jacket, in the manner to be described farther on. Efficient packing b is fitted in the periphery of the main piston B. Efficient packing 1), similar to the packing I), but of less diameter, is titted in the exterior of the cylindrical extension or trunk B. It makes a steam-tight contact with the interior ofa smaller cylindrical portion, A, ofthe fixed portion. This portion A is smoothly finished in its interior, and the packing b plays backward and forward within it in the same manner as the packing of the larger piston B plays within its cylinder A.

Parallel to the packing b, and farther from the main piston B,is an independent packing,

' This is compressed by a gland, B operated by bolts and nuts, or other ordinary or suitable means. This extra packing is, under ordinary conditions, to be compressed but slightly by its gland U is the steam-chest. The steam from the boiler is admitted not directly into the chest, but is compelled first to traverse through the steam-jacket a It enters the steam-jacket through the pipe G. (See Fig. 2.) The principal portion of the steam reaches the steamjacket through two passages, a (see Fig. 1,) which form the termination of the steamjacket a A small portion reaches the steam-chest through a small orifice, 0. This takes the steam from a portion of the steam-jacket a which would otherwise be stagnant, and would allow air to accumulate. By making the orifice a of small area the main current of steam is compelled to traverse the mainportion of the steam-jacket a but a sufficient quantity is admitted through the more direct route to insure acirculation and the constant presence of hot steam therein.

D is the slide-valve, operated by a rod, d, to which is knuckled an eceentricrod, D, receiving motion from an eccentric on the main shaft M. The valve has a large amount of lap on the side farthest from the shaft.

The cylinder-face is marked A A port, 0, leads from the cylinder-face to the annular space around the trunk B. A port, 0", leads from the cylinder-face to the opposite end of the main cylinder. An exhaust-port, 6 leads from the cylinder-face by a lateral passage out into the atmosphere or into a condenser.

The valve is worked with the ordinary motion and at the proper time gives live steam from the boiler to a small annulus on one face of the piston, and afterward admits the same steam to expand on the whole of the opposite side of the piston. \Vhen the trunk-piston B B has completed its outstroke the steam is exhausted through the port 0 J is a strong connecting-rod taking hold of the main crank in the shaft M and playing up and down in the snifieient opening in the outer end of the trunk B. The end which takes hold of the piston is provided with cylindrical trunnions J J, rigidly attached to the connecting-rod and oscillating in hearings in the main piston, the movable brasses B of which are adjusted by screws L, leading therefrom to the outer end of the trunk and when adjusted held rigidly by jam-nuts L. lprefer to let the screws L bear against intermediate shoes, 1), instead of causing them to bear directly upon the adjustable hrasses B It is practicable to so compress the outer packing, b, on the trunk B that it shall serve as a steam-tight packing. In such case it may serve as auxiliary to the main packing 1), arresting any steam which passes the latter through any imperfection or failure; but I prefer, under ordinary circumstances, that the packingbshall be lightly compressed and shall serve mainly as a wiper and lubricator. ()il can be supplied to it at suitable intervals by moving the piston into its extreme outward position and supplying oil through an oil-hole.

To obtain the best effects of my invention the steam should be superheated before it is taken into the jacket around the cylinder. By thus operating at a temperature above that due to the pressure of the steam the temperature of the cylinder and all the parts is raised and maintained at a point nearly equal to that of the superheated steam and a trifle above that due to the pressure of the steam. Under these conditions the steam will not condense in the cylinder nor in the jacket, and all the loss due to the alternate condensation and ree aporation of the water in those parts is avoided.

When it is not practicable to supply steam slightly superheated I employ a reducin g--valve (not shown) at any convenient point in the passage from the boiler to the jacket, which has the well-known efl'ect of increasing the dryness of the steam. It also gives a uniformity to the impelling force of the steam in the engine, which greatly aids in obtaining a uniform speed of the engine. The engine thus conditioned may have a delicate speed-governor in addition; or on some kinds of work where the resistance is uniform it may be worked successfully without the governor. If, notwithstanding theincreased dryness of the steam, due to this reduction of the pressure, there shall be a small amount of water of condensation produced in the jacket, such water may be taken out by a steam-trap.

Any ordinary reducing-valve and any ordinary steamtrap may be used.

Modifications maybe made in the forms and proportions without departing from the principle or sacrificing the advantages of the invention.

hat I have termed the trunnions Jare formed by driving a single straight cylindrical bolt through a close-fitting hole in the end of the connecting-rod; but they may be otherwise attached or forgedinonethcrewith,ifpreferred.

The smoothly-bored extension A from the main cylinder lies close to the exterior of the trunk B. This is important in economy of steam, but is not absolutely essential. It serves as a guide for the trunk and as a means of attaining a steam-tight union of the cylinder therewith through the medium of the packing b. This packing b of the trunk, as also the packing b of the main piston, may be any ordinary or suitable piston-packing. Steam-packingby which I mean metallic packing urged outward by the pressure ofthe steam itselt'admitted within it through suitable passagesmay serve.

My engine is capable of working with either high or low velocity. It may be made large or small. I esteem it especially important for small engines, giving a high degree of cfliciency and economy with few parts and small cost for construction and maintenance.

I claim as my invention 1. In a trunk-engine,the combination, with the main piston B and trunk-piston B, of the two packings b and b and the outer packing, 11*, as and for the purposes herein specified.

2. In a trunk-engine, the transverse pin J, fixed in the extremity of the connecting-rod J, in combination with the adjustable brasses B set-screw I1, and jam-nut L, arranged to be operated from the front end of the trunk, as and for the purposes herein specified.

In testimony whereof I have hereunto set my hand, at New York city, N. Y., this 22d day of June, 1882, in the presence of two subscribing witnesses. W

DAVID N. MELVIN.

Vitnesses:

(Jr-mamas O. STn'rsoN, CHARLES 1t. SEARLE. 

